To collect bodily fluid, such as blood, a holder having a hollow bodily fluid collection needle fixed thereto has heretofore been widely used. Patent Literature 1 below discloses a bodily fluid collecting method using a holder of this kind. This bodily fluid collecting method will be described with reference to FIGS. 10 and 11.
First, as shown in FIG. 10, a tubular holder 101 and a bodily fluid-collecting container 102 are prepared. As shown in a cross-sectional view in FIG. 11, a hollow bodily fluid collection needle 103 is fixed to the holder 101 to penetrate the upper end surface of the holder 101. The bodily fluid collection needle 103 has needle tips at both ends. The needle tip 103a at one end is located outside the holder 101, while the needle tip 103b at the other end extends in the interior of the holder 101. Furthermore, a sheath 104 made of an elastic material, such as rubber, is provided to envelop the portion of the bodily fluid collection needle 103 located in the interior of the holder 101. FIG. 11 shows a state that the sheath 104 is compressed so that the needle tip 103b is exposed out of the sheath 104. Before use, the sheath 104 envelops the needle tip 103b. 
On the other hand, to seal an opening 102a at the upper end of the bodily fluid-collecting container 102, a plug 105 is fixed to the bodily fluid-collecting container 102.
The plug 105 includes a plug body 106 made of rubber and a cover member 107 attached to the plug body 106 to cover the outer surface of the plug body 106. A lower end portion of the plug body 106 is press-fitted into the bodily fluid-collecting container 102 to hermetically seal the opening 102a. The top surface of the plug body 106 is provided in the center with a recess 106a. The thickness of a portion of the plug body 106 provided with the recess 106a is made smaller than that of the other portion thereof. This portion having a relatively small thickness serves as a pierceable portion to be pierced through by the bodily fluid collection needle 103. Furthermore, the outer surface of a side part 107a of the cover member 107 is provided with a plurality of vertically extending ribs 107b. The ribs 107b are formed for the purpose of improving the handleability of the bodily fluid-collecting container, such as ease of removal of the plug 105 from the bodily fluid-collecting container 102 after bodily fluid collection and prevention of unexpected rolling of the bodily fluid-collecting container.
In collecting bodily fluid, e.g., in collecting blood in a bodily fluid-collecting container which is a vacuum blood collection tube, the needle tip 103a at one end of the bodily fluid collection needle 103 is inserted into a blood vessel. The blood is thus introduced into the bodily fluid collection needle, but at this point of time the blood introduced into the bodily fluid collection needle 103 never leaks out because the sheath 104 envelops the needle tip 103b. In this state, as shown in FIG. 11, the bodily fluid-collecting container 102 having the plug 105 fixed thereto is inserted into the holder 101. While in this state the bodily fluid-collecting container 102 is continued to be inserted, the needle tip 103b pierces through the pierceable portion as shown in FIG. 11. Since the interior of the bodily fluid-collecting container 102 is reduced in pressure, the blood is drawn through the bodily fluid collection needle 103 into the bodily fluid-collecting container 102.